This invention relates generally to assembly of optical modules. More particularly, it relates to a mechanism for packaging optically interconnected assemblies requiring of structural stability and precision alignment by using adjustable plugs.
For most optoelectronic products manufactured today, coupling light into or out of an optical device is accomplished by active alignment of one device with respect to another. The basic process is to move an object in space angularly and laterally to locate a first device (X,Y,Z) and orient (xcex8x, xcex8y, xcex8z) it with respect to a second device. The device can be held either by mechanical clamp or suction generated by vacuum pump. Special toolings are usually made for particular geometry.
To maintain alignment, the first device has to be permanently fixed on a motherboard. The challenge is to find a suitable mounting technique that will allow sufficient angular and lateral offset as the fixture secured to a motherboard. There are usually arbitrary gaps formed between bonding surfaces of the optical device and the motherboard, as depicted in FIG. 1 of prior art, due to physical impression of parts. In FIG. 1, a first optical device is aligned respect to a second optical device to couple the light into or out of these optical devices. The gap between surface 1 of the first device and surface 2 of the motherboard is formed. These gaps inhibit the aligned assembly from being assembled with solid contacts.
FIGS. 2, 3, and 4 demonstrate various prior art assembly concepts to compensate for such angular and lateral deviations. Typical solutions involve the use of thick epoxy and/or solder and precision spacers. FIG. 2 shows the gap between two bonding surfaces is filled with epoxy. The problem with this approach is that epoxy shrinks during curing. The resulting dislocation could be significant if the gap is large. This shrinkage is generally predictable and could be accounted for in final assembly. However, this can make the assembly process complicated and often unreliable. FIG. 3 depicts enhanced approach that uses a spacer to reduce the overall gap between the optical device and the motherboard. A layer of epoxy fills the subgap between the optical device and the spacer. The thickness of the spacer has to be precise to properly align the first device with respect to the second. Furthermore, shrinkage of the epoxy during curing is still a problem. Another approach, shown in FIG. 4, is to use a solder bump, allowing two surfaces to be bonded with solder reflow at high temperature. Although many advantages of this technology have been realized: high yield, high strength and self-alignment during joining, the initial setup cost is extremely high. Furthermore, the device is not secured to the motherboard during solder reflow and may become misaligned as the solder solidifies. In addition, the solder bump may not be able to withstand large temperature fluctuations due to differences in the coefficients of thermal expansion of the bonding materials. The problem becomes aggravated as the size of solder becomes larger.
There is a need, therefore, for a low cost packaging method to assemble pre-aligned optical modules to a common substrate, by which the optical modules are permanently fixed on the common substrate without dislocation due to temperature variations.
Accordingly, it is a primary object of the present invention to provide an actively alignable optoelectronic package having high performance characteristics and low manufacturing cost.
It is a further object of the present invention to reduce the requirement of dimensional tolerances on parts or completely eliminate the need for precision spacers.
It is an additional object of the invention to prevent the shrinkage of epoxy in the gap between the bonding surfaces during temperature variations.
It is another object of the present invention to provide a solution to compensate any arbitrary lateral and angular misfits during final mounting.
It is another object of the present invention to use plugs as an adjustable spacer between device carriers and motherboard to compensate possible misalignment.
It is an additional object of the present invention to provide solid contacts and create a rigid aligned structure between modules.
These objects and advantages are attained by apparatus and packaging methods to assemble optical modules to a common substrate with adjustable plugs.
In accordance with a first embodiment of the present invention, the apparatus for attachment and alignment optical devices to a motherboard comprises a device carrier, at least three adjustable plugs, and a filler material. The plugs are configured to fit into openings in the device carrier or the motherboard. A filler material, such as epoxy or solder, fills the space between the device carrier and the motherboard. The device carrier has one or more sides containing the openings. The plugs are typically in the form of the pins or balls with the cross-sections providing maximum contact area such as round or square cross-sections.
The device carrier and the plugs are generally made from materials with low thermal expansion such as aluminum, ceramic, hardened steel, glass, or silicon. These materials will not expand or contract much with the temperature fluctuations, so the overall thermal performance is enhanced. To enhance soldering technique, the plugs could also be plated for soldering or are made from the soldering materials such as tin-lead and gold-tin.
According to a second embodiment of the present invention, a method is set forth for attachment and alignment optical devices to a motherboard to compensate any arbitrary lateral and angular misalignment during the final mounting. In this method, at least three through holes are provided in the device carrier. The plugs are inserted through the holes from the top of the device carrier. The device carrier is aligned spatially and angularly relative to the motherboard. The plugs are tacked to the motherboard and the device carrier to secure the alignment of the device. The filler material fills the gap between the device carrier and the motherboard. The filler material and the plugs secure the device carrier to the motherboard. The plugs and the holes have cross-sections that provide maximum contact area such as square/square cross-sections or round/round cross-sections. The plugs closely fit into the holes, so the clearance is large enough for plugs to slip through the holes without much insertion force. Through holes are provided in the assembly to confine epoxy or solder at the joints between the device carrier and the plugs and form a channel for plugs to slide up and down during movement of the device carrier relative to the motherboard. In this method, the plugs are used as an adjustable spacer between the device carrier and the motherboard.
Furthermore, according to a third embodiment of the present invention another method for attachment and alignment of optical devices to a motherboard to compensate any arbitrary lateral and angular misalignment during the final mounting. This method is similar to the method in the second embodiment as described above, except the through holes are provided in the motherboard, and the plugs are inserted through the holes from the bottom of the motherboard.
Embodiments of the apparatus and methods for attachment and alignment of optical modules allow sufficient angular and lateral offset as the fixture secured to a motherboard. Furthermore, the methods of the present invention reduce the requirement of dimensional tolerances on parts or completely eliminate the need for precision spacers.